Wood or plastic drill bit, with conical reamer

Abstract

The present invention relates to a wood or plastic drill bit, in particular for railway sleepers, comprising a drilling area configured to create a hole, a cylindrical part (2) configured to evacuate the chips and a conical part (3), configured to both form a cone and to evacuate the chips. This drill bit is particular in that it comprises at least two helical knives which each extend continuously from the drilling area, along the cylindrical part (2), and along the conical part (3). Abstract figure: Figure No. 3

Description

Title of the invention: Wood or plastic drill bit, with conical reamer

[0001] The present invention lies in the field of wood or plastic drill bits. It relates to a wood or plastic drill bit with a conical reamer at the end of drilling.

[0002] Wood drill bits with a conical reamer are used in particular for drilling railway sleepers, to create the hole allowing the insertion of lag screws. These lag screws have a cone on the part close to their head, and therefore require that the drilling carried out also has such a cone at the entrance to the drilling.

[0003] Document FR1070059 describes such a drill bit with a single drilling spiral, and two cutting edges on the conical reamer, defining a main groove in continuity with the groove of the spiral, and responsible for evacuating the chips resulting from the drilling, and a smaller secondary groove, making it possible to contribute to the evacuation of the chips resulting from the conical machining.

[0004] However, such a wick has the disadvantage of breaking frequently, particularly at the transition to the cone, in the event of intensive use.

[0005] Document FR2811606 describes a wood drill bit with a conical reamer, with a modified drilling area, making it possible to avoid chip jamming.

[0006] These bits all have the disadvantage of a fragile point between the cylindrical part and the conical part, which causes the bits to break, particularly in intensive use.

[0007] An object of the present invention is to provide a wood or plastic drill bit with a conical reamer which makes it possible to avoid at least one of the drawbacks of the state of the art.

[0008] Another object of the present invention is to provide a wood or plastic drill bit with a conical reamer which reduces the risk of breakage, and which allows more intensive use, in particular for railway sleepers.

[0009] The present invention thus provides a wood or plastic drill bit for railway sleepers comprising a drilling zone configured to create a hole, a cylindrical part configured to evacuate the chips and a conical part, configured to both form a cone and to evacuate the chips, characterized in that it comprises at least three helical knives which each extend continuously from the drilling zone, along the part wrapped in a cylinder, and along the part wrapped in a cone.

[0010] Thanks to these provisions, the risk of breakage is reduced, which allows more intensive use.

[0011] According to other characteristics: • the ratio of the thickness of the knives to the spacing between two knives, measured at the periphery of the cylindrical part and parallel to the longitudinal axis of the cylindrical part, may be at least 1 to 2, which makes it possible to obtain a significant reinforcement of the wicks, • the evacuation spaces can be continuous at the transition between the cylindrical part and the conical part, which improves the reinforcement, • the machined surface of the bit may have a rounding at the intersection between the cylindrical part and the conical part, so as to avoid the presence of an angle, which further improves the reinforcement of the bits, • the pitch of the helical knives can be greater than half the length of the cylindrical part, which gives longer service lives, • the pitch of the helical knives can be greater than the length of the cylindrical part, which gives even longer service lives, • said bit can comprise exactly three helical knives, which gives particularly interesting results, • the thickness of the knives in the conical part can increase less quickly in proportion to the diameter of the conical part, which also allows the reinforcement of the bits.

[0012] The present invention will be better understood on reading the detailed description which follows, with reference to the appended figures in which:

[0013] [Fig-1] [Fig. 1] is a side view of a wood drill bit according to the state of the art

[0014] [Fig. 2] [Fig. 2] is a sectional view of the wood drill bit according to the condition of the technical.

[0015] [Fig.3] [Fig.3] is a side view of a wood drill bit according to the invention

[0016] [Fig.4] [Fig.4] is a sectional view of the wood drill bit according to the invention.

[0017] [Fig.5] [Fig.5] is a side view of a wood drill bit according to a second mode of carrying out the invention

[0018] [Fig. 6] [Fig. 6] is a sectional view of the wood drill bit according to a second embodiment of the invention.

[0019] [Fig. 1] and 2 show a wood drill bit according to the state of the art. There is shown a central threaded point 1, configured to penetrate first into the wood to be drilled, then to pull the drill bit into the material by the effect of the thread and the rotation of the drill bit, a cylindrical part 2, configured to transport the shavings from the end of the drill bit to a conical part 3, configured to form a cone at the entrance to the drilling.

[0020] Within the scope of the present invention, it is possible to provide drill bits without a central threaded point 1, which can be replaced for example by a conical end as for drill bits for drilling metal, or by a quadrangular end.

[0021] A knife has a piercing end 4, a cylindrical helix 5, and a truncated cone helix 6. A core 7 is arranged at the longitudinal axis of the bit, to ensure sufficient support and strength of the helix.

[0022] On the circumference of the wick, the ratio of the thickness of a knife to the space with the adjacent knife is of the order of 1 to 1.5. A thinner knife may not have sufficient mechanical strength.

[0023] For example, for a drill bit according to the invention with a diameter of 14 mm, it is possible to have a helix pitch of 25 mm, a knife thickness, measured parallel to the longitudinal axis of the drill bit of 10 mm, with a spacing with the following knife, measured parallel to the longitudinal axis of the drill bit of 15 mm.

[0024] [Fig. 2] shows a section of the wick in its cylindrical part 2. This section has a support 8, reaching, within a predefined clearance, the circumference of diameter D, and an evacuation space 9.

[0025] In the conical part 3, the support is provided with two blades 10 configured to machine the wall of the hole, and enlarge it. One of them is in the continuity of the knife of the cylindrical part 2, the other is added in the conical part 3, to contribute to the machining of the cone.

[0026] With such a drill bit according to the state of the art, breaks are observed at the transition between the cylindrical part 2 and the conical part 3.

[0027] Whether the section of the knife is increased to increase its resistance, or whether it is reduced, the bits continue to break.

[0028] The inventor carried out numerous tests with different shapes of the wick.

[0029] The invention consists of adding at least one knife to have at least two at the total, preferably add two knives to have three in total.

[0030] The inventor observed that with two knives, the wicks break less, and with three knives, the result is even better.

[0031] The inventor observed this improvement by increasing or decreasing the overall section of the wick.

[0032] The wicks therefore hold better, and break less, even if there is a little less evacuation volume, due to the minimal material needed to make the additional knives.

[0033] [Fig. 3] to 6 show two wood drill bits according to the invention, with two knives in [Fig. 3] and 4, with three knives in [Fig. 5] and 6. There is seen a drilling end 4, comprising, in the example shown, a central threaded point 1, configured to penetrate first into the wood to be drilled, then to pull the drill bit into the material by the effect of the thread and the rotation of the drill bit, a cylindrical part 2 configured to evacuate the chips produced by the drilling end 4, then a conical part 3, configured in the form of a conical reamer 3 to enlarge the hole, to evacuate the chips formed by this enlargement, and to evacuate the chips arriving from the cylindrical part 2.

[0034] The presence of the threaded tip 1 in the drawing is part of an exemplary embodiment. It is also possible, within the framework of the invention, to have other drilling ends, in particular conical as in drills for metals or quadrangular.

[0035] The term "cone" or "conical" is used herein in a broad sense including what would be a truncated cone, or a truncated conical portion.

[0036] Furthermore, the expressions "cylindrical part" and "conical part" are used to express that the geometric envelope of the bit is cylindrical in the "cylindrical part", and that the geometric envelope of the bit is conical or frustoconical in the "conical part". As will be specified below, there is matter and void in this "cylindrical part" and this "conical part".

[0037] At least two knives each have a drilling end 4, a cylindrical helix 5, and a truncated conical helix 6. The helices interpenetrate, and are connected to a central shaft 7 of the drill bit.

[0038] The central shaft 7 is defined here as a part close to the longitudinal axis of the wick in which there is continuous material.

[0039] [Fig.4] and 6 each show a section of the wick at the transition from its cylindrical part 2 to its conical part 3. This section has at least two supports 8, reaching, within a predefined clearance, the circumference of diameter D, and at least two evacuation spaces 9.

[0040] Contrary to expectations, it is not necessary to ensure a cumulation of evacuation spaces 9 of larger volume, nor a cumulation of evacuation spaces 9 of smaller volume, to obtain a better resistance of the wicks. On the contrary, entirely satisfactory results are obtained without significantly varying the total volume of the evacuation spaces 9.

[0041] The inventor has observed during his numerous tests that it is preferable not to increase the speed of advance of the drill bit in the hole too much compared to the speed practiced with a drill bit of the state of the art. This is how better prolonged holding of the drill bits is obtained.

[0042] In the conical part 3, the at least two supports 8 are provided with blades 10 configured to machine the wall of the hole, and enlarge it. The evacuation spaces 9 enlarge as the diameter D increases, which makes it possible to evacuate both the chips coming from the drilling end 4, and those produced by the blades 10 to form the cone.

[0043] According to a preferred embodiment of the invention, measured on the circumference of the bit, parallel to the longitudinal axis of the bit, the ratio of the thickness of a knife to the space with the adjacent knife is less than 1 / 2.

[0044] For example, for a drill bit according to the invention with a diameter of 14 mm and three knives, it is possible to have a helix pitch of 50 mm, a knife thickness, measured on the section of the drill bit of 5 mm, with a spacing with the following knife, measured on the circumference of the drill bit, parallel to the longitudinal axis of the drill bit of 12 mm.

[0045] According to another example, for a bit according to the invention with a diameter of 14 mm and two knives, it is possible to have a helix pitch of 50 mm, a knife thickness, measured on the circumference of the bit, parallel to the longitudinal axis of the bit, of 8 mm, with a spacing with the following knife, measured on the circumference of the bit, parallel to the longitudinal axis of the bit, of 17 mm.

[0046] According to another example, for a drill bit according to the invention with a diameter of 14 mm and three knives, it is possible to have a helix pitch of 120 mm, a knife thickness, measured on the circumference of the drill bit, parallel to the longitudinal axis of the drill bit, of 10 mm, with a spacing with the following knife, measured on the circumference of the drill bit, parallel to the longitudinal axis of the drill bit, of 30 mm.

[0047] The inventor has observed during his numerous tests that a long pitch is advantageous for improving the hold of the wicks. Improved results are obtained with a pitch of at least half the length of the cylindrical part 2.

[0048] The inventor observed that even better hold of the wicks is obtained with a pitch greater than the length of the cylindrical part 2.

[0049] According to the invention, the evacuation spaces 9 are continuous at the transition between the cylindrical part 2 and the conical part 3.

[0050] According to a particular embodiment of the invention, the volume of the evacuation space 9 increases in the conical part 3.

[0051] According to a preferred embodiment of the invention, the machined surface of the bit has a rounding at the intersection between the cylindrical part 2 and the conical part 3, so as to avoid the presence of an angle.

[0052] Although the above description is based on particular embodiments, it is in no way limiting of the scope of the invention, and modifications may be made, in particular by substitution of technical equivalents or by different combination of all or part of the characteristics developed above.

Claims

Claims

1. Wood or plastic drill bit, in particular for railway sleepers, comprising a drilling area configured to create a hole, a cylindrical part (2) configured to evacuate the chips and a conical part (3), configured to both form a cone and to evacuate the chips, characterized in that it comprises at least three helical knives which each extend continuously from the drilling area, along the cylindrical part (2), and along the conical part (3).

2. A drill bit according to the preceding claim in which the ratio of the thickness of the knives to the spacing between two knives, measured at the periphery of the cylindrical part (2) and parallel to the longitudinal axis of the cylindrical part (2) is at least 1 to 2.

3. A wick according to any preceding claim, wherein the discharge spaces (9) are continuous at the transition between the cylindrical portion (2) and the conical portion (3).

4. A drill bit according to any preceding claim, wherein the machined surface of the drill bit has a rounding at the intersection between the cylindrical portion (2) and the conical portion (3), so as to avoid the presence of an angle.

5. A drill bit according to any preceding claim, wherein the pitch of the helical knives is greater than half the length of the cylindrical portion (2).

6. A drill bit according to any preceding claim, comprising exactly three helical knives.

7. A drill bit according to any preceding claim, wherein the pitch of the helical knives is greater than the length of the cylindrical portion (2).

8. A drill bit according to any preceding claim, wherein the thickness of the cutters in the conical portion (3) increases less rapidly in proportion to the diameter of the conical portion (3).

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